1. Field of the Invention
The present invention relates to an optical recording reproducing device, and in particular to a tray structure for an optical recording reproducing device which can improve a reproducing ability of the device and reduce vibration and noise by uniforming a resistance generated when a fluid is contacted with each portion of the disc received and rotated on a tray.
2. Description of the Background Art
A disc, one of the widely-used recording media, is divided into a disc having a diameter of 12 cm (hereinafter, referred to as xe2x80x98general discxe2x80x99) and a disc having a diameter of 8 cm (hereinafter, referred to as xe2x80x98compact discxe2x80x99). A general disc receiving unit and a compact disc receiving unit are held in a recess of the tray which receives the two kinds of discs.
Referring to FIGS. 1 and 2, a general disc receiving unit 2 for receiving a general disc 5 is shown as having a recessed portion.
In addition, a compact disc receiving unit 3 for receiving a compact disc has a comparatively greater recess in a center portion of the general disc receiving unit 2, forming a concentric circle with the general disc receiving unit 2.
A pickup unit 4 is formed expansively from the center portion of the receiving surfaces 2a, 3a of the disc receiving units 2, 3 to an outer surface thereof.
A spindle motor (not shown) for rotating the mounted disc, and a pickup (not shown) for linear movement in the pickup unit 4 and reading a signal recorded in the mounted disc, are formed at the lower portion of the pickup 4.
The recording surface of the disc is positioned separately from the receiving surface of the disc receiving unit by a predetermined distance so that the disc can be smoothly rotated at a predetermined velocity by driving of the optical recording reproducing device.
The structure of the disc receiving units 2, 3 will now be described in detail with reference to FIG. 2.
A first protrusion 2b is formed along the outer circumferential portion of the general disc receiving unit 2.
When the user mounts the general disc 5 on the general disc receiving unit 2, the first protrusion 2b prevents the lower surface of the general disc 5 which is the recording surfaces 5a, 5b where information is recorded from being contacted with the receiving surfaces 2a, 3a, thereby preventing the general disc 5 from being damaged or contaminated by foreign substances.
In more detail, the information is not stored in every portion of the lower surface of the disc. That is, non-recording surfaces 5c, 5c where the information is not stored, are formed at an outer circumferential portion and a center portion of the disc, respectively.
Accordingly, when the general disc 5 is mounted on the general disc receiving unit 2, the non-recording surface 5c formed at the outer circumferential portion of the general disc 5 is supported by the first protrusion 2b, thereby preventing the recording surfaces 5a, 5b of the general disc 5 from being contacted with the first and second receiving surfaces 2a, 3a. As a result, there is a lesser chance that the general disc 5 will be damaged or contaminated by foreign substances.
Similarly, a second protrusion 3b is formed at the outer end portion of the compact disc receiving unit 3, and thus prevents the recording surface of the compact disc from being contacted with the second receiving surface 3a, thereby preventing the compact disc from being damaged or contaminated by foreign substances.
The driving operation of a general disc in a conventional tray structure for the optical recording reproducing device will now be explained.
When the general disc 5 is mounted on the general disc receiving unit 2, and the optical recording reproducing device is driven, the general disc 5 is rotated at a predetermined velocity by rotation of a spindle motor.
Here, the pickup is moved along the recording surfaces 5a, 5b of the general disc 5 which is being rotated, reading the information stored in the general disc 5, and then reproducing the information for the user.
However, the general disc 5 may contact fluid existing between the recording surfaces 5a, 5b thereof and the receiving surfaces 2a, 3a of the receiving units 2, 3, which results in serious vibration and noise. The degree of the vibration and noise is dependent upon the rotational velocity of the general disc 5 and the pressure of the fluid in contact with the general disc 5.
That is, the fluid existing at a static state in a certain space maintains an identical pressure, and thus does not cause noise and vibration. However, if the general disc 5 is rotated at a high velocity, a resistance generated when the recording surfaces 5a, 5b of the general disc 5 are contacted with the fluid is increases, thereby causing noise and vibration.
In addition, when the general disc 5 is rotated, if the space where the fluid exists is small, a pressure of the fluid becomes high, and as a result the resistance generated by the contact of the fluid and the disc is increased, thereby causing considerable vibration and noise.
It will now be described in more detail.
The compact disc receiving unit 3 of the tray 1 is more recessed than the general disc receiving unit 2. Accordingly, when the general disc 5 is mounted on the tray 1, the distance between the inside recording surface 5a of the general disc 5 and the second receiving surface 3a is greater than the distance between the outside recording surface 5b of the general disc 5 and the first receiving surface 2a. 
That is, when the general disc 5 is rotated, the fluid having a high pressure is applied to the outside recording surface 5b of the general disc 5, as compared with the inside recording surface 5a thereof. Therefore, the resistance generated on the recording surface of the general disc 5 is higher on the outside recording surface 5b than the inside recording surface 5a. 
On the other hand, as shown in FIG. 3, each unit of the disc which is rotated at a predetermined angular velocity has a different linear velocity.
That is, the angular velocity indicating a degree of an angle varied by a unit time according to rotation of the disc is identical from the rotation center of the disc to the outer circumferential portion thereof.
However, the linear velocity indicating a length of a distance varied by a unit time according to rotation of the disc is different in each part from the rotation center of the disc to the outer circumferential portion thereof.
For example, referring to FIG. 3, while a region a of the inside recording surface 5a of the general disc 5 is varied to a region axe2x80x2 for a predetermined time, a region b of the outside recording surface 5b is varied to a region bxe2x80x2. Accordingly, the linear velocity is less at the rotation center side of the general disc 5, and more at the outer circumferential portion thereof. The linear velocity is thus greater at the outside recording surface 5b than at the inside 5 recording surface 5a. 
That is, when the disc is rotated, the linear velocity gets increased from the center portion of the disc to the outer portion thereof. As a result, the outer portion of the disc having a higher linear velocity is in greater contact with the fluid, and thus receives more resistance by the fluid.
As discussed earlier, when the general disc 5 mounted on the tray 1 is rotated, the linear velocity of the outside recording surface 5b of the general disc 5 is higher than that of the inside recording surface 5a thereof. In addition, the distance between the outside recording surface 5b and the first receiving surface 2a is smaller than the distance between the inside recording surface 5a and the second receiving surface 3a. Accordingly, the resistance generated when the general disc 5 is contacted with the fluid is greater on the outside recording surface 5b than the inside recording surface 5a. 
Therefore, the conventional tray structure of the optical recording reproducing device has a disadvantage in that the resistance generated when fluid contacts with each portion of the disc mounted and rotated on the tray is not regular, and thus the disc does not smoothly rotate, thereby causing vibration and noise.
Moreover, when the optical recording reproducing device requiring a high precision is driven, the vibration of the disc reduces a precision of the pickup reading the information recorded on the disc.
In addition, the vibration and noise decrease reliability of the device, and often cause a trouble.
It is therefore a primary object of the present invention to provide a tray structure for an optical recording reproducing device which can reduce vibration and noise by uniforming a resistance generated when a fluid contacts with each portion of the rotating disc which is being rotated.
It is another object of the present invention to provide a tray structure for an optical recording reproducing device which can improve reliability of the device by reducing a resistance generated when a fluid contacts with each portion of the rotating disc which is being rotated.
In order to achieve the above-described objects of the present invention, there is provided a tray structure for an optical recording reproducing device wherein a distance between each receiving surface of the tray for receiving and reproducing recording media having a different size and the recording medium is identical at a rotation center portion of the recording medium and an outer circumferential portion thereof.
In addition, in order to achieve the above-described objects of the present invention, there is provided a tray structure for an optical recording reproducing device including: a first receiving unit for receiving a first recording medium; and a second receiving unit for receiving a second recording medium which is larger than the first recording medium, and forming a concentric circle with the first receiving unit, a distance between a receiving surface of the first receiving unit and the recording medium being identical to a distance between a receiving surface of the second receiving unit and the recording medium.
In order to achieve the above-described objects of the present invention, there is provided a tray structure for an optical recording reproducing device wherein a distance between a receiving surface of the tray for receiving and reproducing a recording medium and the recording medium is increased from a center portion of the recording medium to an outer circumferential portion thereof.
Also, in order to achieve the above-described objects of the present invention, there is provided a tray structure for an optical recording reproducing device wherein a distance between a receiving surface of the tray for receiving and reproducing a recording medium and the recording medium is gradually decreased according to a rotation direction of the recording medium.